CHR70 Pensil boxes: anechoic measurments

[markaudio]

Hi Guys,
While I was busy these last months, Evan had a little time to run some enclosure experiments with the support of Plack Audio, a local box maker. Evan and Mr. Ning (Plack boss) tried some experiments using a new CHR70A (more about this driver later) and a series of pensil boxes.

They built various boxes, including a standard Pensil and anechoically tested them.

Take a look at the pics. You'll see a standard box, a larger/narrower box and a 2 driver box. I've attached the RAW (Note the word "RAW") frequency curves.

Interestingly, I did get a couple of hours with these boxes in a descent listening room at Plack. Note all boxes were operated with No filters of ANY kind (passive, active or anything else). Along with 2 Plack technicians, all favoured the standard box, but only by a whisker. The dual driver box did particularly well, increased SPL, almost mill-pond flat response with it lush beefy bass. I also like the hybrid single driver box. Its bass went a lick lower than the standard box design, but was a little softer. In all, a very nice effort by the guys and a very interesting set of experiments.

All credit to Scott. These basic experiments do much to vindicate his expertise and design knowledge.

If there's allot of interest in the hybrid boxes, I'l try to beg for the drawings from the 2 guys.

A reminder chaps that these boxes are very basic, made from 15-mm MFD with no bracing, yet they've produced promising results.

Cheers
Mark.

[Scottmoose]

I'm a happy camper with the measured responses.

If there's sufficient interest, I'll do an optimised twin driver version.

[chrisb]

Originally Posted by Scottmoose

I'm a happy camper with the measured responses.

If there's sufficient interest, I'll do an optimised twin driver version.

can one be top firing?

[toobhed]

Does having the second driver firing from the top avoid comb filtering? Are the effects of comb filtering what I see in the 15k-20k response drop in twin cabs graph that looks opposite to the a rise in 15k-20K response in the two single driver cabs? Admittedly and academic question as my ears drop off around 14k...

Mario

[markaudio]

Hi Mario,
Re the twin driver set-up, there was no audible combing effect from the test boxes. The listening distance was around 3.3 metres. Combing should not be an issue on 2 driver close mount set-ups of this type with listening distances greater than 2 metres.

Specifically in the 15-kHz to 20-kHz range, its not possible to specifically identify this effect as the boxes used only 15-mm MDF and weren't braced. However, I'd normally expect to see a flatter response from set-ups of this type, making it useful for those with bigger rooms and/or requiring more power-handling.

Thanks
Mark.

[markaudio]

Originally Posted by chrisb

can one be top firing?

Hi Chris,
Maybe problematic since these boxes remain Damped Air Coupled (all be it non-optimised alignments) whereby driver positioning is exacting; But Scott is the main man to answer this question. He's kindly offered to do a twin design if enough folks request it.

Personally, the twin box did allot better than I expected. I reckon its worth a build, especially for cross-over stereo/HT. Imaging 4 of these + a CHR sealed centre box, could be very nice HT me reckons.

Cheers
Mark.

[markaudio]

Hi Chris,
I've made a new thread for the woofer comment and moved the posts. Sorry I forgot to keep you short comment on up-firing, please feel free to re-post that part of your comment on this thread.

Cheers
Mark.

[chrisb]

Originally Posted by markaudio

Hi Chris,
I've made a new thread for the woofer comment and moved the posts. Sorry I forgot to keep you short comment on up-firing, please feel free to re-post that part of your comment on this thread.

Cheers
Mark.

no worries, one of those posts was an acknowledgment of my own that I already knew the answer to the question of floorstander MLTL with one up-firing driver - I've been living with them for a couple of years now

[skeeter99]

I'd be interested in a dual box for sure!! Love the look and I'm guessing would be good surrounds for my Supers I was already thinking about that after looking at Graham's site a month or so ago.

Scott

[toobhed]

Thank you Mark for the well written reply,
Mario